Fractionating column



c..1. scHlLLING :TAL 2,701,710

mcnom'rmc commu Feb. 8, 1955 Original Filed Sept. 23, 1945 2Sheets-Sheet INVENTORS FIG.

' ATTORNEY Feb- 3, 1955 c. J. scHlLLlNG Erm. 2,701,710

FRACTIONATING COLUMN 2 Sheets-Sheet 2 Original Filed Sept. 28, 1945 C.J.SCHILLING L.S TWOMEY INVENTORS ATTORNEY United ,States Patent OFRACTIONATING COLUMN Clarence J. Schilling, Allentown, Pa., and Lee S.Twomey, Vista, Calif., assignors to Air Products, Incorporated, acorporation of Michigan 7 Claims. (Cl. 261-114) The present inventionrelates generally to fractionating columns and more specifically tomeans for subdividing a stream of liquid to be contacted with gas in acolumn into a plurality of streams of which the volumes aresubstantially equal.

This application is a division of an application entitled FractionatingColumns filed by Clarence J. Schilling and Lee S. Twomey on September28, 1945, under Serial No. 619,110. The present application containsonly that portion of the original specification which is relevant toliquid distributing means.

An object of the invention is to providel means for distributing one ormore of the uid feeds to an air or gas fractionating column among aplurality of noncommunicating bubbling wells formed on or in afractionating late.

P An object of the invention is to provide a simple and effective meansfor subdividing a single stream of a liquid into a plurality of streamsof equal volume or of predetermined volumetric relation, and in whichthedivided or lesser streams will maintain a constant volumetric relationregardless of variations in the volume of the supplying stream.

An 'object of the invention is to provide a stream-subdividing meanshaving the characteristics above described, together with means formaintaining the distributing `orifices free from solids carried insuspension and which otherwise tend to accumulate in the orifices anddisturb the desired volumetric relation between the plural streams.

Modern liquid fractionation is performed, almost without exception, inbubble plate columns. In their conventional form, these columns flow thereflux liquid across the plate and around all the bubble caps fixed init. In columns even of small diameter and having a correspondingly smallnumber of caps per plate, much difficulty is experienced in producingeven flow and distribution of the reflux liquid, without which thehighest etllciency cannot be attained. As the diameter of the plateincreases, the efficiency of the plate tends to decrease, by reason ofpoorer liquid distribution over its area. If for any reason, as forexample buckling of the plate or settling of the column, the platedeparts appreciably from a horizontal plane, its efficiency falls offvery rapidly and the plate becomes nonfunctional when the departure fromhorizontality is only a few degrees.

Further, in very large columns the plates usually employed have anefficiency somewhat lower than those in smaller units, because of thehydraulic gradient needed to cause the liquid to flow at the necessaryvelocity across a wide plate. This results in a liquid depthdisadvantageously greater at the upstream than at the downstream edge ofthe plate. Through the employment of the invention herein described, theplate may be divided into a number of sections, as regards liquid flow,of such dimensions as in large measure to avoid differences in depth andthe resultant lowering of efficiency, avoiding the necessity forconstructing a number of smaller complete columns.

The invention comprises a novel form of fractionating column proper inwhich the plates are provided with a plurality or multiplicity ofpockets or wells, each feeding reflux liquid without redistribution intoa well in the plate next below, in combination with a novel andeffective means for distributing the liquid feed or supply stream amongthe wells on the uppermost plate and with certain accessories which tendto maintain the desired distribuice tion unimpaired and which permit thedistributing device to be flushed out with only a momentary interruptionto the functioning of the column.

The invention will best be understood with reference t'o the attacheddrawings and the following description thereof, in which:

Fig. 1 is a vertical section through a single-stage air 'fractionatingcolumn embodying the basic features of the invention;

Fig.l 2is a plan section through the upper end of the column, as on theline 2-2 of Fig. 1;

Fig. 3 is a plan section through the column at the level indicated at3-3 of Fig. 1;

Fig. 4 is a plan section through the column at the level indicated at 44 of Fig. l;

Fig. 5 is a vertical section through the/,upper end of l a column,illustrating certain modifications of and additions to the details shownin Fig. 1; and

Fig. 6 is an outline diagram of a two-stage column in which theinvention may be utilized, this figure illustrating the merger andredistribution of segregated liquid streams.

Referring first to Fig. l, the invention is illustrated in this figureas applied to a single-stage fractionating co1- umn, such as is oftenused in the fractionation of liquid air. This column consists of threefunctionally distinct sections: the distributing section A, thefractionating section B and the reboiling section C. The inventionresides in the distributing section and in the structure and arrangementof plates in the fractionating section, the reboiling section beingconventional.

Air previously compressed, dried and precooled by means not shown isintroduced at 10 into a boiling coil 11 immersed in a bath 12 of liquidoxygen. In this coil, the air is liquefied in supplying heat to theoxygen vath which is thus continuously boiled. The liquid air thenpasses through a conduit 13 and an expansion valve 14 by which it isbrought to a lower pressure. The expanded liquid, together with anyvapor evolved due to pressure reduction, are introduced into the upperend of the column as at 15, the liquid descending over and through the.plates in a manner to be described. The vapor flashed ofi by pressurereduction, together with that separated by fractionation on the plates,escapes from the upper end of the column as at 16; this is anitrogenrich vapor usually referred to as gaseous nitrogen though it isnever entirely pure. The oxygen separated by the plates in a desiredpurity and usually referred to as product oxygen is withdrawn from thelower end of the column, either as a liquid at 17 or as a vapor at 18,as may be preferred. To this point, the structure and steps describedare well known and are no part of the instant invention. y

The liquid entering the column at 15, being liquid air enriched inoxygen, descends over a funnel-shaped member 19 into an annular feedwell 20, formed by concentric spacing of a feed tube 21 and a nitrogenvent tube 22. The feed tube is provided with a lower ring of meteringperforations 23 and with an upper ring of overflow perforations 24. Thesize of the metering perforations is so adjusted (in the construction ofthe apparatus) that the liquid level 25 will lie below perforations 24during normal operation, these openings being provided as a spillway inthe event of flooding of the feed tube. The number of openings 24 isimmaterial and one will suli'ice if of sufficient area to care for themaximum flow. It is preferable that the liquid level should lie abovethe metering perforations with the feed stream at normal size.

Theliquids flowing through the individual perforations 23 of the lowerring pass into corresponding compartments 26 formed' by the insertion ofpartitions 27 in a ringshaped tray 28. Each of these compartments isprovided with a drain tube 29 extending into one of the bubbling wells30 in the uppermost fractionating plate 31. The tray is illustrated asattached both to the feed tube and to the inner wall 32 of column shell33, an'd the drain tubes are illustrated as sealing in liquid in thebubbling wells. Both of these arrangements are matters of convenienceonly, as the tray maybe supported in any dethe distribution out ofbalance.

sired manner and the drain tubes may, if preferred, be prilviled withindividual sealing cups or even left unse e The structure just describedwill divide a liquid feed stream (using that word--in the sense of anystream which is fed onto a fractionating plate, regardless of itsorigin) into any desired number of individual or lesser streams whichwill have a substantially constant volumetric relation. Ordinarily theperforations will have the saine net area and will deliver substantiallyequal streams. By reason of the relatively small diameter ofA the liquidcolumn in the. feed tube, the hydraulic head on perforations occurringon opposite sides of the tube differs only very slightly even when thecolumn is inclined. It is possible and might under some circumstances beadvantageous to give the perforations different net areas to supplystreams of different volumes, the volumetric relationship of which wouldbe constant.

It has been found that small orifices, such as those indicated at 23,are liable to reduction in area or to stoppage by accumulation of icecrystals (for example, of water or carbon dioxide), particularly if thearrangements for caustic washing and drying of the air supply are notfully effective. The supply stream may also contain foreign matter suchas pipe scale, metallic oxides, etc., which tend to restrict or tobridge the perforations and throw If this condition is anticipated, itis desirable to place a fine screen 34 over the top of funnel 19 to stopthe larger particles. ,f'

As a further precaution, such fine sediments as may pass the screen andtend to accumulate in the perforations may be dislodged and carriedthrough by vibrating or reciprocating a solid body within the orifice.Fig. 1 shows an arrangement for this purpose which is adapted to use intruck-mounted or shipboard columns which, in their use, are subjected tovibration or oscillation. This device consists of a number of wires 35,preferably resil-v ient, projected through the perforations from a`suspended ring 36. This ring is swingingly supported from funnel 19 orfeed tube 21 by light rods 37 which may Well be looped at their ends.The wires are of less diameter than the perforation and remain withinit, and are considered in figuring the net area of the remaining annularorifice.

The vibration of apparatus mounted on a truck or the swaying motion towhich a shipboard column is subject cause ring 36 to swing relative tothe column through small arcs and the wires to vibrate and also toreciprocate through short distances, keeping the orifices free fromsediments. The wires are also subjected to vibration by the flow ofliquid around them. In the case of stationary columns, not subject tomovement due to transportation or water support, a similar arrangementmay be used if mechanical provision is made for imparting a vibratory oroscillatory movement to the ring by power or by the hand of the operatorthrough a suitable seal. Or a solid body may be passed through andwithdrawn from each orifice at intervals, as described in connectionwith Fig. 5 to follow.

Fig. 5 illustrates several variations from the structure abovedescribed. Thus, the tray 28 is attached only to the feed tube orchamber Z1 leaving an annular space 38 for the upward passage of vapor.This permits nitrogen forming a sediment wellor trap as at 45.

vent tube 22 to be dispensed with, a fianged opening 39 being providedin its stead for the passage of vapor through the funnel. Theseparticular variations are unimportant and merely indicative of numerousways in whichthe structure of Fig. 1 may be varied within the scope ofthe invention, but others are of more importance.

This figure illustrates a form of orifice clearing mechanism especiallyadapted to use in large stationary columns. In this form, eachperforation 23 is provided with a clearing plug 40 which is of such sizeas 'ust to pass through the orifice and is preferably pointed orguidance into the orifice. A wire brush maybe used instead of the solidplug if preferred. Element 40 is carried by arod 41 which in turn isfixed in the armature 42 of a solenoid 43. Either inside or outside thecolumn shell 33 is a Sylphon bellows 44 into the free end of which therod or armature is sealed to prevent escape of va r. 0n energizing thesolenoid, the armature is drawn into the coil and the plug or brush 40is passed through the orifice, clearing away accumulations of sediment,the plug being withdrawn when the solenoid circuit is broken. Thesolenoids, if more than one is used, may be connected in parallel forsimultaneous actuation through a 4 hand switch or they may be actuatedin rotation by any automatic timing switch.

This orifice clearing mechanism replaces the ring 36 and the vibratingwires 35 of the form of Fig. 1 and is intended to be illustrative of avariety of manual and automatic .devices which may be used for thispurpose. The essential is to provide means for keeping the orificesclear a s without such means the distributor will be subject tointerruption and disturbance of proper functioning.

Again, even with the provision of a screen, it has been found thatfibres of valve packing, fragments of metallic oxides and other solidsmay collect in the feed tube 2l and interfere with or stop thedistribution of the feed stream. To care for this condition, if any,when it should occur, it is desirable to continue the feed tubedownwardly to a considerable distance below perforations 23,

To the lower portion of the trap is connected a conduit 46, preferably"passing through the outer column we ll 33, the conduit being providedwith a manual valve 47. Through this conduit the liquid contained infeed well 21 may be withdrawn at intervals, flushing out any solidscollected in the trap. Any gas which may follow will er assist inclearing the trap of sediment.

By opening the expansion valve cautiously, while the nitrogen and oxygenoutlets are closed or restricted, any desired pressure, within thelimits of safety, may be built up and maintained in the column. Openingvalve 47 meanwhile will effectually flush out trap 45.

ln order to provide a means for back-flushing the orices 23simultaneously with the trap, it is desirable to provide a manuallyoperable valve for closing the inlet of the feed well while the ushingoperation is being performed, thus limiting the communication fromcolumn to trap to that afforded by the orifices 23, through which thevapor within the column must pass to escape. thus providing aneffective, simultaneous flushing of orifices and trap. This means may beof simple construction, as for example a cup-shaped valve 48 arranged toenter the upper end of tube 21 and to seat on a shoulder 49 formedinside the tube below the level of perforations 24. This valve isnormally held in an elevated position. as shown in solid lines in thefigure, by a stirrup 50 and a pair of levers 51 and 52 coupled to acommon shaft, lever 52 being outside the column.

To blow out the sediment trap, the nitrogen discharge 16 is interruptedby closing a valve at some point outside the column, and valve 47 isopened. Lever 52 is then raised, allowing valve 48 to drop to theposition indicated by dotted lines, at which the upper end of the feedwell is closed. A material part of all the liquid contained in thecolumn will thereafter vaporize and, if desired, the blowing back of thesediment trap may be continued until the column is dry, or it may beinterrupted whenever the discharge of sediment ceases.

To prevent liquid liowing from the funnel into the feed well fromsidetracking through the upper perforations duringnoperation, an annulartray 53 may be fixed to the feed we Under some circumstances, notablywhere a side stream enters the column, it is necessary to merge all ofthe Segre gated streams and to redistribute the merged stream. Thissituation is illustrated in Fig. 6, showing a two-stage column. As isconventional in columns of this type, high pressure nitrogen, liquefiedby the reboiling condenser 62, is passed to the upper end of the 'columnand onto a distributor 55 by which it is divided among the wells on theuppermost plate of low pressure fractionating section 56.

The runbacks from the wells on the lowermost plate of this section aremerged in a liquid pool which is illustrated as collected on a blindplate 57 having an opening surrounded by a dam 58 4through which vaporpasses upwardly and the merged stream ows downwardly onto a seconddistributor 59 which also receives the side stream of crude oxygenpassing up through conduit 60 from the base of the tower. The purpose ofthe pool is solely to seal the drain tubes from the plate above, whichmay be individually sealed if preferred. By the second distributor 59,the mixed stream of runback and side feed is divided among the wells onthe uppermost plate in fractionating section 61.

The liquid nitrogen produced by the reboling condenser 62 is in partcollected on a tray 63 from which the nitrogen stream above described iscarried through conduit 64 tothe upper end of the column. The excessover the quantity required to reflux the low pressure plates voverflowsonto a distribu-tor 65 by which it is divided among the wells on theuppermost plate of high pressure fractionating section 66. The lowermostplate of this section drains into the pool 12 of crude oxygen in thebase of the column. Compressed and cooled air is introduced into thecolumn at 67, product oxygen is removed at 68 and gaseous nitrogen at69, all in the customary manner.

We claim:

1. In a fractionating column, means for dividing a liquid stream into aplurality of lesser streams having a substantially constant volumetricrelation, comprising: a substantially circular chamber adapted toreceive said stream and having a row of drainage perforationssubstantially horizontally disposed in its wall; a ring materialsurrounding and spaced from said chamber and so suspended as to swingrelative to the column when said column is rocked, and a resilient wireprojected from said ring into each of said perforations, said wire beingof less diameter than said perforation to leave an annular orifice forthe passage of liquid.

2. In a fractionating column, means for dividing a liquid stream 'into aplurality of lesser streams having a substantially constant volumetricrelation, comprising: a chamber adapted to receive said stream andhaving a plurality of drainage perforations through its wall; a elementpassed through each said perforation, said element being of suchcross-section as to leave an annular orifice for the flow of liquid,means supporting the elements in the column for movement into and out ofthe perforations including inertia means movably mounted relative to thecolumn and operatively connected to the elements for moving the elementsrelative to the chamber responsively to movement of the column.

3. In a liquid-gas contact column having means providirig a plurality ofseparate liquid-gas contact paths and means for introducing at apredetermined rate of flow a liquid stream to the column, a distributorfor dividing the introduced liquid stream among a plurality of separatestreams and for feeding the separate streams to separate liquid-gascontact paths, comprising an elongated liquid receiving chamber forreceiving the introduced liquid stream, means for mounting the chamberin the column with its lower portion above the liquidgas contact pathsand with its longitudinal axis lying substantially along the verticalaxis of the column, a plurality of metering orifices in the lowerportion of the chamber, each of .the orifices having an inletcommunicating with the liquid in the chamber and an outlet-communicatingto without the chamber, the orifices being located in a substantiallycommon plane perpendicular to the vertical axis of the column, meansfor-maintaining a liquid head in the chamber above the orifices at thepredetermined rate of H ow of the introduced liquid stream, means formaintaining a substantially uniform head acting on the liquid leavingthe`distributor through each of the orifices, means for conducting gasvflowing upwardly from the liquid-gas contact paths past the chamber, andliquid conducting means for conducting liquid flowing from the orifices.to separate liquid-gas contact paths irrespective of deviations of thecolumn from a vertical position, the last-named means'including aplurality of feed conduits each leading to a separate liquid-gas contactpath and each including an inlet located below the plane of the orificesand a plurality of liquid conductors connected between separate'orificesand the inlet of separate feed conduits, the liquid-conductors e havinga liquid conducting wall communicating direc its respective orifice,each liquid conducting wall including a portion of material imperviousto upwardly flowing gas displaced from a plane passing through theeolumn'perpendicular to its vertical axis, and the liquid lconductingmeans being segregated from eachother with 'respect to liquid.

4. In liquid gas contact column, a distributor for dividing a liquidstream among a plurality of separate to the outlet of descending gascontact paths, comprising: a chamber of substantial depth and having adiameter less than the diameter .of the columnpositioned in the columnto receive the stream, a plurality of drainage orifices in the lowerportion of the chamber, the liquid flow characteristics of the orificesand the effective liquid holding depth of the chamber being such thatwith normal liquid flow rates a head of liquid is maintained at alltimes in the chamber above the orifices but the chamber does notoverflow, and means impervious to upwardlyl flowing gas positionedbetween the chamber and the column wall for conducting the liquiddraining from eachgorifice to one only of the descending gas contactpaths, the chamber having an annular cross section taken in a horizontalplane to permit ascending gas to rise therethrough.

5. In a liquid gas contact column, a distributor for dividing a liquidstream among a plurality of separate descending gas contact paths,comprising: a chamber of substantial depth and having a diameter lessthan the diameter of the column positioned in the column to receive thestream at its upper end, a plurality of drainage orifices in the lowerportion of the chamber, the liquid flow characteristics of the orificesand the effective liquid holding depth of the chamber being such thatwith normal liquid flow rates a head of liquid is maintained vat alltimes in'the chamber above the orifices but the chamber does notoverflow, and means impervious to upwardly flowing gas positionedbetween the chamber and the column wall for conducting the liquiddraining from each. orifice to one only of the descending gas contactpaths, means for conducting upwardly flowing gas past the'upper end ofthe chamber and means forming a communication between the liquiddraining from each orifice and within the chamber above the surface ofthe liquid in the chamber.

6. In a liquid-gas contact column having means providing a plurality ofseparate liquid-gas contact paths, a distributor of the characterdefined in claim 3 including means positioned in the column for cleaningthe metering orifices.

7. Ina liquid gas contact column, a distributor for dividing a liquidstream among a plurality of separate descending gas contact paths,comprising: a chamber of substantial depth and having a diameter lessthan the diameter of the column positioned in the column to receive thestream, the`chamber having an appreciably greater depth than width, aplurality of drainage orifices in the lower portion of the chamber, theliquid flow characteristics of the orifices and the effective liquidholding depth of the chamber being such that with normal liquid flowrates the head of liquid is maintained at all times in the chamber abovethe orifices but thechamber does not overflow, means for conductingtheliquid draining from each orifice to one only of the descending gascontact paths, a solici member positioned for relative movement into andout of each of the orifices, an inertia responsive ring surrounding thechamber and pivotally connected to the column for swinging movementrelative to the column upon deviation of the column, and meansconnecting each solid member to the ring for moving eatli solid memberresponsively to deviation of the co umn.

References Cited in the file of this patent

1. IN A FRACTIONATING COLUMN, MEANS FOR DIVIDING A LIQUID STREAM INTO APLURALITY OF LESSER STREAMS HAVING A SUBSTANTIALLY CONSTANT VOLUMETRICRELATION, COMPRISING: A SUBSTANTIALLY CIRCULAR CHAMBER ADAPTED TORECEIVE SAID STREAM AND HAVING A ROW OF DRAINAGE PERFORATIONSSUBSTANTIALLY HORIZONTALLY DISPOSED IN ITS WALL; A RING MATERIALSURROUNDING AND SPACED FROM SAID CHAMBER AND SO